Active vs. Passive

[TerryVierhout]

The solar energy is one of the ideal sources of renewable energy. This energy can be used incessantly as long as there is sun. It is believed that the earth absorbs nearly 3,850,000 exajoules (EJ) of solar energy. In one hour, the energy absorbed by the planet's oceans and landmasses is more energy than the world consumes in an entire year. With lower costs and increased efficiency of solar technologies, solar energy is becoming a rage in renewable energy market.

Solar energy can be tapped in two ways: Passive and Active. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and positioning buildings to maximize sun exposure. Active solar techniques use photovoltaic panels, pumps, and fans to convert sunlight into electricity.

Active technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies. Investment in solar energy can be done keeping in mind the favorable aspects of tapping sun’s energy and the ways of doing it.

[fizzissist]

~360watts per square meter.

How'd I do?

[mozmozmoz]

Originally Posted by fizzissist ~360watts per square meter. How'd I do?

I dunno, what was the question? If you're talking insolation, 1000W per square metre peak, 250 average, but it depends a lot on all sorts of stuff.

My answer is: passive. Every time.

I'll accept a fan or pump if I have to, but since so much of the energy I use I want as heat it makes little sense to use intermediate forms with large conversion losses. I'm hanging out for the heat-powered air conditioning units to be available in smaller sizes because a 10kW unit would turn my house into a freezer. I suppose I could run the solar heating to counter it

[fizzissist]

...The minimum power output, not the peak or average, is the main factor governing solar power’s economic viability. The capital cost would be 25 times more than nuclear power. The least-cost solar option would require 400 times more land area and emit 20 times more CO2 than nuclear power...

http://carbon-sense.com/wp-content/u...-realities.pdf

[Geof]

Originally Posted by fizzissist ...The minimum power output, not the peak or average, is the main factor governing solar power’s economic viability. The capital cost would be 25 times more than nuclear power. The least-cost solar option would require 400 times more land area and emit 20 times more CO2 than nuclear power... http://carbon-sense.com/wp-content/u...-realities.pdf

What!! Heresy, Blasphemy; to the stake with the un-believer.

[mozmozmoz]

Originally Posted by fizzissist The least-cost solar option would require 400 times more land area and emit 20 times more CO2 than nuclear power...

Sure, since all they're talking about is the hardware. Take into account the lifecycle cost of the whole system and nuclear falls apart. And of course since we don't have nuclear powered mining machines we still need fossil fuels to run our mines etc, and in Australia their water consumption is a bit of an issue. Then if you like we can talk about the waste problem, and how breeder reactors are another theoretically possible thing that have been ten years away for the last thirty years. Excuse me, I'm feeding the trolls again.

[Geof]

Originally Posted by mozmozmoz .....and how breeder reactors are another theoretically possible thing that have been ten years away for the last thirty years. Excuse me, I'm feeding the trolls again.

Breeder reactors are not theoretical they are real. The reason they have not been used is because the fuel they use/produce can also be used for weapons.

[martinw]

Hello,

1100 watts per square metre is the maximum incoming solar radiation if you are sitting on top of Mount Everest on a cloudless day with your green energy gizmo pointing directly at the sun.

Oh dear, at altitudes where ordinary mortals dwell, there are clouds, and , at less than ideal times, there is daytime and night. Alas, the green gizmo probably does not track the sun either. So what is the average level of solar radiation available to a static gizmo optimally aligned? In the UK, I would hazard a guess at a lot less than 100 watts per square metre over the course of a year, day and night.

What is the conversion efficiency of PVs or water collectors ? About 10% tops overall.

You do the math, as they say...

Best wishes,

Martin

[Geof]

Originally Posted by martinw ....What is the conversion efficiency of PVs or water collectors ? About 10% tops overall....Martin

You are too pessimistic I think. PV starts out at 15% or a bit higher for some of the newer stuff and I am not sure it degrades to 10% for a number of years.

Thermal collectors can be well over 50% depending on the exit temperature but I think the best overall for thermal through all the steps to electricity is in the region of 20% using focussing collectors and steam turbines.

[martinw]

Originally Posted by Geof You are too pessimistic I think. PV starts out at 15% or a bit higher for some of the newer stuff and I am not sure it degrades to 10% for a number of years. Thermal collectors can be well over 50% depending on the exit temperature but I think the best overall for thermal through all the steps to electricity is in the region of 20% using focussing collectors and steam turbines.

Dear Geof,

OK my figures are ball park. I will not argue with the PV efficiencies. The solar water heating figures are based on flat panel domestic installations in the UK. There was a report published about six years ago which indicated a net yield of 2500 kWh per year from a number of (approx.) 1.5 metre square roof mounted panels. That represents a saving of about £120 a year at off-peak electricity rates. The installations typically cost £2000+ to install. Add to that, the cost of capital, maintainance and depreciation, and the economics look grim.

Large scale concentrating, industrial plants are a different ball game, but in terms of land useage, I would guess that the efficiency in output per metre square is no better than a domestic panel on the roof of a house.

Tin hat time...

Best wishes,

Martin

[Mariss Freimanis]

Far from ideal; solar energy is a miserable energy source. If it were, everyone would be falling all over themselves to replace oil with solar. That isn't happening so it means one of two things. Either people are too stupid to know what's good for them or there is something wrong with the premise of "free and renewable" solar energy. I humbly submit it's the latter.

Solar is 1,000W peak and 250W average per meter^2 insolation. At a 10% conversion efficiency, it is 100W peak, 25W average per meter^2, or 0.6 kWh per day on average. The sun doesn't shine at all at night and it shines poorly at dawn and dusk.

An average US household consumes 10,000 kWh per year or 27kWh per day. It would take a 180 meter^2 (1,920 ft^2) solar cell collector to meet this demand. Why so big? The sun doesn't shine at night. Forget about it on snowy, cold days in January. Sad fact #1: Electricity cannot be stored.

About storage batteries. It would take a 2,250 Ah 12V battery to store a day's worth of electricity use. That's 40 automotive type batteries and if it's overcast for 10 days, make it 400 batteries.

Solar cell panels cost about $5 per Watt uninstalled. 4,500W peak is needed so that's $22,500 uninstalled. Automotive batteries are about $100 for the 60Ah variety so that's another $40,000. Add $5,000 for the inverter (got to have AC instead of DC) and add another $10,000 for installation and wiring. You will need a special ventilated room in your house for all those batteries. You are up to $80,000 now just to set up a realistic solar energy home; I didn't count the value of the former bedroom you gave up to turn into the battery room. Sad Fact #2: Free, renewable solar energy costs a lot.

Automotive batteries last about 5 years. You have 400 of them. You will be replacing one every 5 days. Who sweeps the snow off of your solar collector in the winter? Who sweeps the leaves off in the fall? Who washes the dust off during the summer? Who repairs corroded wiring that is exposed to the elements? Who replaces panels when cells go bad? They are silicon after all; ever had a blown transistor? Figure on $8,000 a year in maintenance. Sad Fact #3: Complex systems cost $$$ to maintain them in a working condition.

Solar cell panels, inverters and batteries don't grow on ecologically friendly and renewable trees. They are manufactured. Their manufacture is energy intensive and involves the use of many "toxic" chemicals. Sad Fact #4: The up-stream pollution costs for all down-stream environmentally friendly solutions have to be taken into account.

There are over 300 million people in the US. Let's call that 75 million 4-people households. $80,000 times 75 million is 6 trillion dollars. The US GDP is 14.3 trillion dollars making this "investment" nearly 50% of the GDP for installation and 5% of the GDP for annual maintenance. Sad Fact #5: Free solar energy will make everyone poor.

Nuclear energy is the only sane choice once oil runs out and becomes too expensive. It integrates with the existing power grid.

Other than that, I'm all for solar energy. My Texas Instruments TI-36X scientific calculator runs off of a solar cell. Sadly a misname because it's never powered by the sun but rather incandescent light-bulbs and fluorescent lighting. I rarely have the inclination to use it at the beach so I don't bring it along. It is in fact a fossil fuel powered calculator.

Mariss

[martinw]

Dear Mariss,

Absolutely...

Best wishes,

Martin